The invention relates to a prosthetic knee assembly that pivots in a single axis, and in particular to a knee assembly having a two-stage, weight activated hydraulic valve body and linkage that accommodates normal gait and also stabilizes the knee against shock and/or during strenuous or other movement requiring knee flexion.
Prior art hydraulic prosthetic knee assemblies have typically utilized a single valve chamber. The assemblies allow the knee to pivot freely when raised during normal gait. When loaded with the user""s weight, the single chamber controls the gait speed (i.e. leg swing) and partially dampens the relatively soft walking forces. Gait control hydraulic assemblies are shown at U.S. Pat. Nos. 4,775,037 and 4,662,486 that provide duplex movement of a pair of pistons in two cylinders.
The prior art devices, however, limit the physical activities of the user. They are particularly not designed to accommodate physical activities requiring leg/knee flexion, such as during stair transitions or encountered in many physical sports, for example skiing, snowboarding, skateboarding, volleyball or other sports where high stress forces are periodically encountered during landings. An improved assembly is therefore desired to provide greater knee stability and accommodate more active lifestyles.
The present prosthetic knee assembly includes a socket, harness or other suitable mechanism to attach to the user. A pylon and suitable prosthetic foot depend from the prosthetic knee assembly. An intermediate pivot joint and two-stage hydraulic shock member and cooperating linkage stabilize the knee during flexion and accommodate both soft and hard shock loads.
The prosthetic knee of the present invention provides an assembly that includes a two stage hydraulic cylinder. Cylinder operation is controlled by a linkage that translates relative upward forces exerted on the foot and the rotation of the knee joint to direct hydraulic flow and piston action at the available stages. One stage provides an adjustable rebound force or extension assistance that offsets the user""s normal gait pattern. That is, the knee pivots freely, when raised, and a first piston biased by an adjustable soft spring directs fluid flow to provide sufficient force to control gait speed and partially offset the user""s weight when the foot contacts the ground. The second stage includes a second piston biased by a spring with a heavier weight spring that is activated by knee flexion and provides a relatively greater offsetting force to stabilize knee rotation, such as during stair transitions, when landing from jumps or encountering other shock loads. The user is thereby provided greater stability for activities requiring knee flexion under load conditions and is able to engage in a wider range of physical activities, such as skiing and other sports that stress the legs.
It is accordingly a primary object of the invention to provide a prosthetic knee capable of providing several different levels of reactionary or offsetting support forces relative to physical activity to maintain user stability, for example, gait control and shock absorption.
It is a further object of the invention to provide a prosthetic knee support control having several stages that offer several adjustable ranges of reactionary or offsetting support forces.
It is a further object of the invention to provide a prosthetic knee having an adjustable two-stage hydraulic control wherein a first stage responds with approximately 50 to 100 lbs. of support for light duty activities and a second stage responds with approximately 250 to 600 lbs. of support for more strenuous activities, such as stair transitions, skiing, snowboarding.
It is a further object of the invention to provide a prosthetic knee with a hydraulic control wherein a cam-actuated linkage, upon experiencing knee flexion or rotation in excess of 5 degrees of rotation, switches fluid flow relative to first and second spring biased pistons.
It is a further object of the invention to provide an actuator body that responds to load forces at the leg to pre-set a piston and moveable piston chamber to respond to enhanced loading and re-direct flow within a multi-chambered cylinder.
The foregoing and other objects, advantages and distinctions of the invention are obtained in a prosthetic leg assembly having a suction socket, prosthetic foot, pylon and improved prosthetic knee. A single-axis knee joint assembly includes a plunger-activated, three-chamber cylinder body, a control valve body, a control valve actuator, a pylon shaft and artificial foot.
The knee joint assembly rotates in a single axis and provides a two-stage hydraulic gait control and shock absorption system that is activated by the weight of the wearer during use. The load forces on the knee cause a plunger to travel in a first cylinder and direct fluid flow as determined by control and actuator valve bodies to selectively pass through second and/or third cylinders containing spring biased pistons. Hydraulic fluid is directed to pass to either a second cylinder containing a xe2x80x9csoftxe2x80x9d spring and/or into a third cylinder containing a xe2x80x9chardxe2x80x9d spring, depending upon the force exerted on the activator body by the pylon shaft and flexion experienced by the knee. Two different levels of adjustable shock absorption or offsetting forces are applied in response to stabilize the user. Adjustment controls are provided at the soft and hard spring cylinders and control valve body. The actuator valve body includes a floating piston and piston chamber.
Alternative microprocessor directed electronic and hydraulic controllers are disclosed that can be adapted to a knee assembly to sense myoelectric activity and physical movement at the prosthesis, such as rotation, strain, and/or linear movement and appropriately stabilize joint movement.